A frequent source of operating problems in refining and hydrocarbon processing units is the formation of deposits on the internal metallic surfaces throughout those units resulting in an increase in pressure drop, decrease in efficiency, increase in energy consumption, loss of operating time, and other well-known difficulties. These deposits include salts of ammonia, inorganic contaminants that enter the process in the feed, and deposits that develop as by-products. From corrosion of the processing unit including metal sulfides, metal oxides, metal hydroxides, and other metal salts. These deposits alone or in combination with other hydrocarbon polymers and decomposition products often form deposits that are difficult to remove from the internals of the processing units.
During the processing of hydrocarbon liquids, such as crude oil, at elevated temperatures such as between 200.degree. and 500.degree. F. in a refinery, small amounts of water emulsified or otherwise entrained in the hydrocarbon will first vaporize and then later condense on the metallic surfaces of the overhead equipment of the high temperature units, such as distillation columns. This water contains acidic elements, predominantly hydrochloric acid (HC1), which will corrode the surfaces of the overhead equipment at locations where condensation occurs.
In an attempt to minimize this corrosion, hydrocarbon processors will add chemical compounds to the hydrocarbon prior to elevated temperature processing for the purpose of neutralizing the acid, e.g., HC1. The compound most frequently employed is ammonia. The ammonia will neutralize the HC1 by forming ammonium chloride.
The neutralization of HC1 by ammonia mitigates against the problems of corrosion. However, the formation of ammonium chloride causes others. The ammonium chloride, which is vaporized during elevated temperature processing, is sublimed onto the internal surfaces of the overhead equipment. Sublimation, as herein defined, is intended to mean that the ammonium chloride passes directly from the vapor state to its solid crystaline form, bypassing its liquid phase. Crystaline ammonium chloride builds up on these surfaces resulting in the operational problems previously discussed.
U.S. Pat. No. 4,703,865 (Staley, et al.,) describes a method where low melting point/oxygenated liquid amines are injected in hydrocarbon processing units to remove and/or to prevent the formation of ammonium salt deposits. Furthermore, oxygen containing hydrocarbon compounds are injected in hydrocarbon processing units to remove metal compound deposits. The oxygenated amines and/or the oxygen containing compounds may be injected alone or in combination. In addition, these amines and/or the oxygen containing compounds are used in combination with filming agents which causes corrosion in such units.
U.S. Pat. No. 4,877,578 (Zetlmeisl et al.) discloses the use of the reaction product of an alkylenepolyamine and formaldehyde in a water system containing ammonium chloride, in the hydrocarbon overhead systems of a refinery, for the purpose of inhibiting corrosion. They disclose that the polyamides alone are less effective than the reaction product (col 6, lines 59-62). However, they do not mention the problem of ammonium chloride deposition, by sublimation of the ammonium chloride to the cool parts of the overhead system, and do not teach the use of the polyamines for the purpose of inhibiting such ammonium chloride deposits.
U.S. Pat. No. 4,855,053, Schutt, discloses that ammonium bisulfate deposition may be abated by adding large amounts of ammonium chloride.
It is an object of the present invention to inhibit the growth and/or facilitate the removal of ammonium chloride deposits on the surfaces of the overhead equipment in a hydro-carbon refinery. The aforementioned problems are overcome by the present invention which discloses a method for the complete removal and/or prevention of the formation of deposits of ammonium chloride.